Search Options

Search form

Welcome to the National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

Responses

Planning for adaptation (to address and prepare for impacts) and mitigation (to reduce future climate change, for example by cutting emissions) is becoming more widespread, but current implementation efforts are insufficient to avoid increasingly negative social, environmental, and economic consequences.

Introduction

Actions to reduce emissions, increase carbon uptake, adapt to a changing clim ate, and increase resilience to impacts that are unavoidable can improve public health, economic development, ecosystem protection, and quality of life.

Over the past few years, the focus moved from “Is climate changing?” to “Can society manage unavoidable changes and avoid unmanageable changes?”49,50 Research demonstrates that both mitigation (efforts to reduce future climate changes) and adaptation (efforts to reduce the vulnerability of society to climate change impacts) are needed in order to minimize the damages from human-caused climate change and to adapt to the pace and ultimate magnitude of changes that will occur.51,52,53,54 Adaptation and mitigation are closely linked; adaptation efforts will be more difficult, more costly, and less likely to succeed if significant mitigation actions are not taken.50,55

Key Message

Substantial adaptation planning is occurring in the public and private sectors and at all levels of government; however, few measures have been implemented and those that have appear to be incremental changes.

Key Message

There is no "one-size fits all” adaptation, but there are similarities in approaches across regions and sectors. Sharing best practices, learning by doing, and iterative and collaborative processes including stakeholder involvement, can help support progress.

Key Message

Climate change adaptation actions often fulfill other societal goals, such as sustainable development, disaster risk reduction, or improvements in quality of life, and can therefore be incorporated into existing decision-making processes.

Key Message

Vulnerability to climate change is exacerbated by other stresses such as pollution, habitat fragmentation, and poverty. Adaptation to multiple stresses requires assessment of the composite threats as well as tradeoffs amongst costs, benefits, and risks of available options.

Adaptation

Adaptation actions can be implemented reactively, after changes in climate occur, or proactively, to prepare for a changing climate.1 Proactively preparing can reduce the harm from certain climate change impacts, such as increasingly intense extreme events, shifting zones for agricultural crops, and rising sea levels, while also facilitating a more rapid and efficient response to changes as they happen.

FEDERAL: A November 2013 Executive Order calls for, among other things, modernizing federal programs to support climate resilient investments, managing lands and waters for climate preparedness and resilience, creating a Council on Climate Preparedness and Resilience, and the creation of a State, Local, and Tribal Leaders Task Force on Climate Preparedness and Resilience.2 Federal agencies are all required to plan for adaptation. Actions include coordinated efforts at the White House, regional and cross-sector efforts, agency-specific adaptation plans, and support for local-level adaptation planning and action.

STATE: States have become important actors in national climate change related efforts. State governments can create policies and programs that encourage or discourage adaptation at other governance scales (such as counties or regions)3,4 through regulation and by serving as laboratories for innovation.5,6 Although many of these actions are not specifically designed to address climate change, they often include climate adaptation components. Many state level climate change-specific adaptation actions focus on planning. As of winter 2012, at least 15 states had completed climate adaptation plans; four states are in the process of writing their plans; and seven states have made recommendations to create state-wide adaptation plans.7

TRIBES: Tribal governments have been particularly active in assessing and preparing for the impacts of climate change. Some are using traditional knowledge gleaned from elders, stories, and songs and combining this knowledge with downscaled climate data to inform decision-making.8 Others have integrated climate change into decision-making in major sectors, such as education, fisheries, social services, and human health.9

LOCAL: Most adaptation efforts to date have occurred at local and regional levels. A survey of 298 U.S. local governments shows 59% engaged in some form of adaptation planning.10 Mechanisms used by local governments to prepare for climate change include: land-use planning; provisions to protect infrastructure and ecosystems; regulations related to the design and construction of buildings, road, and bridges; and preparation for emergency response and recovery.11,12,13,14,15,16 Local adaptation planning and actions are unfolding in municipalities of different sizes. Regional agencies and regional aggregations of governments too are taking actions.17,18

Adaptation Example: The Southeast Florida Regional Compact

Miami-Dade County staff leading workshop on incorporating climate change considerations in local planning.

Courtesy Armando Rodriguez, Miami-Dade County

The Southeast Florida Regional Compact is a joint commitment among Broward, Miami-Dade, Palm Beach, and Monroe Counties to partner in reducing heat-trapping gas emissions and adapting to climate impacts, including in transportation, water resources, natural resources, agriculture, and disaster risk reduction. Through the collaboration of county, state, and federal agencies, a comprehensive action plan was developed that includes hundreds of actions. Notable policies include regional collaboration to revise building codes and land development regulations to discourage new development or post-disaster redevelopment in vulnerable areas19

BUSINESS: Many companies are concerned about how climate change will affect feedstock, water quality, infrastructure, core operations, supply chains, and customers’ ability to use products and services.20 Some companies are taking action to avoid risk and explore potential opportunities, such as: developing or expanding into new products, services, and operational areas; extending growing seasons and hours of operation; and responding to increased demand for existing products and services.20,21,22,23,24

NGOs: Non-governmental organizations have played significant roles in the national effort to prepare for climate change by providing assistance to stakeholders that includes planning guidance, implementation tools, explanations of climate information, best practices, and help with bridging the science-policy divide.

See regional sections of this Highlights report for additional examples of adaptation efforts. Selected federal, state, tribal, and local actions appear in the Adaptation chapter of the full National Climate Assessment.

Adaptation to climate change is in a nascent stage. The federal government is beginning to develop institutions and practices necessary to cope with climate change. While the federal government will remain the funder of emergency responses following extreme events for which communities were not adequately prepared, an emerging federal role is to enable and facilitate early adaptation within states, regions, local communities, and the public and private sectors.1 The approaches include working to limit current institutional constraints to effective adaptation, funding pilot projects, providing useful and usable adaptation information – including disseminating best practices, and helping develop tools and techniques to evaluate successful adaptation.

Despite emerging efforts, the pace and extent of adaptation activities are not proportional to the risks to people, property, infrastructure, and ecosystems from climate change; important opportunities available during the normal course of planning and management of resources are also being overlooked. A number of state and local governments are engaging in adaptation planning, but most have not taken action to implement the plans.25 Some companies in the private sector and numerous non-governmental organizations have also taken early action, particularly in capitalizing on the opportunities associated with facilitating adaptive actions. Actions and collaborations have occurred across all scales. At the same time, barriers to effective implementation continue to exist.

Key Message

Carbon dioxide is removed from the atmosphere by natural processes at a rate that is roughly half of the current rate of emissions from human activities. Therefore, mitigation efforts that only stabilize global emissions will not reduce atmospheric concentrations of carbon dioxide, but will only limit their rate of increase. The same is true for other long-lived greenhouse gases.

Key Message

To meet the lower emissions scenario (B1) used in this assessment, global mitigation actions would need to limit global carbon dioxide emissions to a peak of around 44 billion tons per year within the next 25 years and decline thereafter. In 2011, global emissions were around 34 billion tons, and have been rising by about 0.9 billion tons per year for the past decade. Therefore, the world is on a path to exceed 44 billion tons per year within a decade.

Key Message

Over recent decades, the U.S. economy has emitted a decreasing amount of carbon dioxide per dollar of gross domestic product. Between 2008 and 2012, there was also a decline in the total amount of carbon dioxide emitted annually from energy use in the United States as a result of a variety of factors, including changes in the economy, the development of new energy production technologies, and various government policies.

Key Message

Carbon storage in land ecosystems, especially forests, has offset around 17% of annual U.S. fossil fuel emissions of greenhouse gases over the past several decades, but this carbon “sink” may not be sustainable.

Key Message

Both voluntary activities and a variety of policies and measures that lower emissions are currently in place at federal, state, and local levels in the United States, even though there is no comprehensive national climate legislation. Over the remainder of this century, aggressive and sustained greenhouse gas emission reductions by the United States and by other nations would be needed to reduce global emissions to a level consistent with the lower scenario (B1) analyzed in this assessment.

Mitigation

The amount of future climate change will largely be determined by choices society makes about emissions. Lower emissions of heat trapping gases and particles mean less future warming and less severe impacts; higher emissions mean more warming and more severe impacts. Efforts to limit emissions or increase carbon uptake fall into a category of response options known as “mitigation.”

Carbon dioxide accounted for 84% of total U.S. greenhouse gas emissions in 2011.26 The vast majority (97%) of this CO2 comes from energy use. Thus, the most direct way to reduce future climate change is to reduce emissions from the energy sector by using energy more efficiently and switching to lower carbon energy sources.

In 2011, 41% of U.S. carbon dioxide emissions were attributable to liquid fuels (petroleum), followed closely by solid fuels (principally coal in electric generation), and to a lesser extent by natural gas.26 Electric power generation (coal and gas) and transportation (petroleum) are the sectors predominantly responsible.

Achieving the lower emissions path (B1) analyzed in this assessment would require substantial decarbonization of the global economy by the end of this century, implying a fundamental transformation of the global energy system. The principal types of national actions that could effect such changes include putting a price on emissions, setting regulations and standards for activities that cause emissions, changing subsidy programs, and direct federal expenditures. Market-based approaches include cap-and-trade programs that establish markets for trading emissions permits, analogous to the Clean Air Act provisions for sulfur dioxide reductions.

None of these price-based measures has been implemented at the national level in the U.S., though cap-and-trade systems are in place in California and in the Northeast’s Regional Greenhouse Gas Initiative. A wide range of governmental actions are underway at federal, state, regional, and city levels using other measures, as are voluntary efforts, that can reduce the U.S. contribution to total global emissions. Many, if not most of these programs are motivated by other policy objectives – energy, transportation, and air pollution – but some are directed specifically at greenhouse gas emissions, including:

Energy Efficiency: Reduction in CO2 emissions from energy end-use and infrastructure through the adoption of energy-efficient components and systems – including buildings, vehicles, manufacturing processes, applicances, and electric grid systems;

Low-Carbon Energy Sources: Reduction of CO2 emissions from energy supply through the promotion of renewables (such as wind, solar, and bioenergy), nuclear energy, and coal and natural gas electric generation with carbon capture and storage; and

Non-CO2 Emissions: Reduction of emissions of non-CO2 greenhouse gases and black carbon (soot); for example, by lowering methane emissions from energy and waste, transitioning to climate-friendly alternatives to HFCs, cutting methane and nitrous oxide emissions from agriculture, and improving combustion efficiency and means of particulate capture.

Federal Actions

The Federal Government has implemented a number of measures that promote energy efficiency, clean technologies, and alternative fuels.27,28,29,30,31 Sample federal measures are provided in Table 27.1 in the Mitigation chapter in the full report. These actions include greenhouse gas regulations, other rules and regulations with climate co-benefits, various standards and subsidies, research and development, and federal procurement practices.

Weatherization can include installing more efficient windows to save energy.

For example, the Environmental Protection Agency has the authority to regulate greenhouse gas emissions under the Clean Air Act. The Department of Energy provides most of the funding for energy research and development, and also regulates the efficiency of appliances.

The Administration’s Climate Action Plan32 builds on these activities with a broad range of mitigation, adaptation, and preparedness measures. The mitigation elements of the plan are in part a response to the commitment made during the 2010 Cancun Conference of the Parties of the United Nations Framework Convention on Climate Change to reduce U.S. emissions of greenhouse gases by about 17% below 2005 levels by 2020. Actions proposed in the Plan include:

limiting carbon emissions from both new and existing power plants;

continuing to increase the stringency of fuel economy standards for automobiles and trucks;

continuing to improve energy efficiency in the buildings sector;

reducing the emissions of non-CO2 greenhouse gases through a variety of measures;

increasing federal investments in cleaner, more efficient energy sources for both power and transportation; and

identifying new approaches to protect and restore our forests and other critical landscapes, in the presence of a changing climate.

Co-Benefits for Air Pollution and Human Health

Actions to reduce greenhouse gases can also reduce other air pollutants, yielding human health benefits.

Actions to reduce greenhouse gas emissions can yield co-benefits for objectives apart from climate change, such as energy security, ecosystem services, and biodiversity.33,34 In particular, there are health co-benefits from reductions in air pollution. Because greenhouse gases and other air pollutants share common sources, particularly from fossil fuel combustion, actions to reduce greenhouse gas emissions also reduce other air pollutants.

The human health benefits can be immediate and local, in contrast to the long-term and widespread effects of climate change.35 These efforts have been found to be cost effective.35,36 Methane reductions have also been shown to generate health benefits from reduced ground-level ozone.37

City, State, and Regional Actions

Jurisdiction for greenhouse gases and energy policies is shared between the Federal government and states.38 For example, states regulate the distribution of electricity and natural gas to consumers, while the Federal Energy Regulatory Commission regulates wholesale sales and transportation of natural gas and electricity. Many states have adopted climate initiatives as well as energy policies that reduce greenhouse gas emissions. For a survey of many of these state activities, see Table 27.2 in the full report. Many cities are taking similar actions.

The most ambitious state activity is California’s Global Warming Solutions Act, with a goal of reducing greenhouse gas emissions to 1990 levels by 2020. The program caps emissions and uses a market-based system of trading in emissions credits, as well as a number of regulatory actions. The most well-known, multi-state effort has been the Regional Greenhouse Gas Initiative (RGGI), formed by 10 northeastern and Mid-Atlantic states (though New Jersey exited in 2011). RGGI is a cap-and-trade system in the power sector directing revenue from allowance auctions to investments in efficiency and renewable energy.

More than 1,055 municipalities from all 50 states have signed the U.S. Mayors Climate Protection Agreement,39 and many of these communities are actively implementing strategies to reduce their emissions.

Federal voluntary programs include Energy STAR, a labeling program that, among other things, identifies energy efficient products for use in residences and commercial and industrial buildings.

Managing Land for Mitigation

Key Message

Decisions about how to address climate change can be complex, and responses will require a combination of adaptation and mitigation actions. Decision-makers – whether individuals, public officials, or others – may need help integrating scientific information into adaptation and mitigation decisions.

Key Message

Many decision support processes and tools are available. They can enable decision-makers to identify and assess response options, apply complex and uncertain information, clarify tradeoffs, strengthen transparency, and generate information on the costs and benefits of different choices.

Key Message

Ongoing assessment processes should incorporate evaluation of decision support tools, their accessibility to decision-makers, and their application in decision processes in different sectors and regions.

Key Message

Decision Support

As a result of human-induced climate change, historically successful strategies for managing climate-sensitive resources and infrastructure will become less effective over time. Decision support processes and tools can help structure decision-making, organize and analyze information, and build consensus around options for action.

Although decision-makers routinely make complex decisions under uncertain conditions, decision-making in the context of climate change can be especially challenging. Reasons include the rapid pace of changes, long time lags between human activities and response of the climate system, the high economic and political stakes, the number and diversity of potentially affected stakeholders, the need to incorporate uncertain scientific information of varying confidence levels, and the values of stakeholders and decision-makers.42,43,44 The social, economic, psychological, and political dimensions of these decisions underscore the need for ways to improve communication of scientific information and uncertainties and to help decision-makers assess risks and opportunities.

Collaboration: The importance of both scientific information and societal considerations suggests the need for the public, technical experts, and decision-makers to engage in mutual shared learning and shared production of relevant knowledge.44,45

Risk Management: Making effective climate-related decisions requires balance among actions intended to manage, reduce, and transfer risk. Risks are threats to life, health and safety, the environment, economic well-being, and other things of value. Methods such as multiple criteria analysis, valuation of both risks and opportunities, and scenarios can help to combine experts’ assessment of climate change risks with public perception of these risks.46

Decision Support Case Study: Denver Water

Climate change is one of the biggest challenges facing the Denver Water system. Due to recent and anticipated effects of climate variability and change on water availability, Denver Water faces the challenge of weighing alternative response strategies and is looking at developing options to help meet more challenging future conditions.

Denver Water is using scenario planning in its long-range planning process (looking out to 2050) to consider a range of plausible futures involving climate change, demographic and water use changes, and economic and regulatory changes. The strategy focuses on keeping as many future options open as possible while trying to ensure reliability of current supplies.

The next step for Denver Water is to explore a more technical approach to test their existing plan and identified options against multiple climate change scenarios. Following a modified robust decision-making approach,47,48 Denver Water will test and hedge its plan and options until those options demonstrate that they can sufficiently handle a range of projected climate conditions.

NRC, 2009: Informing Decisions in a Changing Climate. National Research Council, Panel on Strategies and Methods for Climate-Related Decision Support, Committee on the Human Dimensions of Global Change, Division of Behavioral and Social Sciences and Education. National Academies Press, 200 pp. URL↩

NRC, 2010: Adapting to Impacts of Climate Change. America’s Climate Choices: Report of the Panel on Adapting to the Impacts of Climate Change. National Research Council. The National Academies Press, 292 pp. URL↩

NRC, 2010: Limiting the Magnitude of Future Climate Change. America’s Climate Choices. Panel on Limiting the Magnitude of Future Climate Change. National Research Council, Board on Atmospheric Sciences and Climate, Division of Earth and Life Studies. The National Academies Press, 276 pp. URL↩

Simmonds, J., 2011: Resource for Consideration by the NCA Teams Addressing the Impacts of Climate Change on Native Communities. Native Communities and Climate Change Project of the University of Colorado Law School and the Cooperative Institute for Research in Environmental Science.URL↩

Wilbanks, T., D. Bilello, D. Schmalzer, and M. Scott, 2012: Climate Change and Energy Supply and Use. Technical Report to the U.S. Department of Energy in Support of the National Climate Assessment. 79 pp., Oak Ridge National Laboratory, U.S. Department of Energy, Office of Science, Oak Ridge, TN. URL↩

National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.